In total knee arthroplasty it is customary to resurface the articulating ends of the femur and the tibia with prostheses which are fastened to the cut and prepared ends of the femur and tibia. One such prosthesis is that described in a catalog published by Johnson & Johnson Orthopaedics Inc. entitled "P.F.C. Total Knee System" (P.F.C. is a registered trademark of Johnson & Johnson Orthopaedics Inc.) using a surgical technique described in a booklet published by Johnson & Johnson Products entitled "Surgical Technique--The Press Fit Condylar Total Knee System with Specialist Instruments." Another such prosthesis is described in U.S. Pat. No. 4,822,366.
One component of the P.F.C. Total Knee System and virtually every other total knee replacement system utilized is a patellar component.
Heretofore great difficulty has been encountered in providing a patellar component which will endure, for extended periods of time, the rigors to which such components are placed. Thus, a patellar component is subjected to continual rubbing against the femoral component of the prosthesis with each flexing movement of the leg. As a result, the patellar component may wear to an extent as to impede function of the knee even though the other components may not be worn out. In addition, it may also cause undue wear on the other components of a total knee system.
In a total knee system, the patellar component is typically a dome-shaped member which is implanted on a flat surface or a recess cut into the patient's patella. The patellar implant may either be all plastic, typically high molecular weight polyethylene (HMWPE) or plastic with a metal backing formed of titanium, chrome-cobalt alloy, stainless steel or the like.
In addition to the patellar implant shown in the Johnson & Johnson Orthopaedics brochure entitled "P.F.C. Total Knee System", other types of patellar implants are disclosed in catalogs published by Dow Corning Wright entitled "Whiteside Ortholoc Modular Knee System" and published by DePuy, Warsaw, Ind., a Division of Boehringer Mannheim Corporation, entitled "The AMK Total Knee System".
As will be appreciated, it is desirable to utilize a patellar implant which combines the advantages of requiring a minimal amount of cutting of the patella, secure placement of the patellar implant and the ability to easily remove such implant in the event revision is required.
Accordingly, it is an object of the present invention to provide a patellar prosthesis for use in combination with the prepared patella bed in which minimal amount of the patient's natural patella is required to be removed.
It is a further object of the present invention to provide a patellar prosthesis designed for implantation in a patella which can be replaced with minimal damage to the patella in the event revision is required.